Herpetofaunal species composition on the Vieques National Wildlife Refuge, Vieques, Puerto Rico

Abstract

The loss of biodiversity is identified as one of the biggest ecological tragedies of our time and two of the groups most affected by this loss are amphibians and reptiles. A thorough inventory and long term monitoring that provides information on species composition and relative abundance are valuable tools to create a baseline for future assessments of population change in conservation areas. This study addresses and evaluates the herpetofaunal composition, abundance and diversity on the Vieques National Wildlife Refuge (VNWR). The study sites were conducted on the east and west areas of the VNWR, which are located within two different ecological life zones: subtropical dry forest (east area) and subtropical moist forest (west area). Amphibians and reptiles were sampled during eight months between April and November, 2008 using a mixture of three capture techniques: drift fences arrays with pitfall traps, double-ended funnel traps and visual encounter survey (VES) transects. All individuals captured using these techniques were marked with alpha numeric fluorescent tags, which provide individual identification. Abundance, richness and diversity were determined in the study sites on the west and east areas during the wet and dry season. Similarity analyses (ANOSIM) for the sampling areas were conducted to determine the existence of seasonal and spatial patterns in the structure of the herpetofaunal community. A correlation analysis was carried out in order to evaluate the relationship between the environmental variables such as precipitation, relative humidity and temperature and the abundance and richness of species. Population size for Anolis cristatellus was calculated using the capture history with models of closed populations and heterogeneous closed populations. An Indicator Species Analysis (ISA) and Similarity Percentage Analysis (SIMPER) were conducted to identify which species characterized the sampling areas, seasons and sampling periods. A total of 3,248 individuals of 11 species, distributed on 4 amphibian and 7 land reptile species were documented using the three capture techniques. The VES transects were the most efficient capture technique in this study providing greater than 95% of all the documented specimens in the east and west areas. The diversity indices calculated was low for both the east and west areas, although the study sites on the east area provided higher species richness and abundance than study sites on the west area. The similarity analysis indicated no significant differences between sampling areas demonstrating that there is no spatial pattern in the composition among the areas; but indicated a seasonal pattern in the community structure between seasons. Anolis cristatellus and Eleutherodactylus antillensis were the most abundant species in both areas of the island. Anolis pulchellus was the species that characterized the east area during nocturnal sampling, while Anolis stratulus characterized the west area during the diurnal sampling. The results of accumulation curves of this study showed a sampling efficiency of 100% for the expected amphibians and reptile species in the west area. The sampling efficiency in the east area documented a 100% of the expected amphibian species and the reptile species presented a 68.6% and 63.2% for the ICE and ACE estimators respectively.